Disc-type

ABSTRACT

A disc-type fibrous cellulosic stock refiner has bar-and-groovetype rotating and stationary refining plates in which the working or bar section has a Di/D0 ratio of between 0.55 and 0.85, and in which the operation of the refiner work input into the stock is analogized to the absorption of energy in a clutch or disc brake.

52 9 I so mill/1' 0 United States Patent l 13,552,664

[72] Inventors William Herbert; [56] References Cited James H. Riedel,Middletown, Ohio UNITED STATES PATENTS 1 PP 740,884 2,035,994 3/1936Sutherland 24l/296X 1 PM June 28,1968 2,537,570 1/1951 Bossert 24l/296 I1 Patsmed 2,589,307 3/1952 Symons 241/296x 1 Asslgnee The m W CmPanY2,971,704 2/1961 .lohansson 241 /256X P 3,032,282 5/1962 Asplund 241/2563 3,117,603 1/1964 Keuren..... 241/29sx 3,241,775 3/1966 Clendaniel24l/296X Primary Examiner-Donald G. Kelly Attorney-Marechal, Biebel,French & Bugg [54] DISC-TYPE REFINERS 5 Clams 6 Drawmg ABSTRACT: Adisc-type fibrous cellulosic stock refiner has [52] US. Cl 241/260bar-and-groove-type rotating and stationary refining plates in I [51lnt. Cl B02c 7/06, which the working or bar section has a D lD ratio ofbetween B02c 7/12 0.55 and 0.85, and in which the operation of therefiner work {50] Field of Search 241/296- input into the stock isanalogized to the absorption of energy 8, 255-6, 260, 162, 163 in aclutch or disc brake.

' 36 n g Q 9 a s2 I 50 L 48 in/ PATENTED JAN 5 I97! SHEET 2 OF 3 FIG-3PATENTEU JAN 5191:

PEG-5 EFFECTIVE PQWER e-w /HP 0836 FRICWQN POWER LQSS CQRRESPOND w nwDISC-TYPE REFINERS BACKGROUND OF THE INVENTION Cellulosic fibers such aspaper pulp, bagasse, insulation or fiber board materials, cotton and thelike, are commonly subjected to a refining operation, which consists ofthe mechanical rubbing of the fibers between sets of relatively rotatingbar and groove elements. In disc-type refiners, these elements haveconsisted of plates having annularly arranged alternate bar-and-groovepatterns formed therein, with the groove pattern extending in a somewhatradial direction, but frequently at some angle to a true radius.

Often, refiners are used to cut or shorten the length of the fibers.Also, where the fibers are already sufficiently short, the refiner maybe used to develop fiber strength, by the working and rubbing of thefibers between the bars. This may open or split the outer wall or shell,and expose a new surface of fresh fibrils, to form fibers capable offorming bonds with other fibers, for increasing the strength, opacity,or other qualities of the resulting product. 1

Traditionally, the design of paper pulp refiners has been dic rated by aconsideration of the number and radial ext'entof refiner bars which canbe placed within a given refiner on the basis that if some refiner barswere desirable, therefore a greater number would be more desirable. Manyformulas and analytical approaches have been proposed to explain theoperation of a refiner, and terms such as inch-cuts-per-minute" weredeveloped as'a measure of refiner performance, on the basis that themore cutting action which can be effected between the bars of therotating and the stationary discs the more refining would result.Inch-cuts-per-minute is a measure of the number of inches of cuttingsurface produced in a minute of time, based upon the rpm. and the amountof cutting surface in a given refiner disc. As a result of this concept,refiners have commonly been made with the bars being extended as long aspractical toward the center of the refiner, with the result that theratio of inside to outside diameter (DJD has commonly been less than 0.5and frequently in the range of 0.45.

Such refining discs with the bars extending one-half or more of theradius of the disc have frequently caused special problems in bardesign, as it is necessary either to stagger groupings of the bars bymaking a plurality of separate plates, or by specially tapering the barsand intermediate grooves, or both Attempts to increase theinch-cuts-per-minute factor have resulted in refiner plates of complexdesign which are expensive to manufacture.

SUMMARY OF THE INVENTION The present invention is the result of a newapproach to the analysis of refiner operation. A new theory of operationof a disc-type refiner has been developed by analogy to the horsepowerformula for clutches and brakes. As a result of this theory, it ispossible to improve the design of a refiner disc by specially selectingthe DJD, ratio to provide the highest degree of refining requiring theleast power input. In other words, a refiner plate design is providedwhich has the least loss for the amount of refining produced.

This is accomplished, by separately considering the work loss factors ina disc refiner, arriving at an optimized and im proved refiner discconstruction which produces more refining, with less loss of energy. Inother words, the refiner of the present invention is one in which moreof the work put into the refiner goes into the stock and less of thework is wasted on nonproductive loss factors.

It is accordingly an important object of this invention to provide adisc-type cellulosic fiber refiner which has refiner plates of improvedefficiency.

Afurther object of the invention is the provision of a disc refiner, andrefiner plates therefor, in which the ratio of inside diameter tooutside diameter of the working portion is between 0.55 and 0.85.

Another object of the invention is the provision of a refiner replacedby the plates of this invention;

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective of a twin disctype refiner constructed according to this invention;

FIG. 2 is an elevational view, partially in section, of the refiner ofFIG. 1;

FIG. 3 is a fragmentary plan diagram of one of the improvements inrefiner plates;

FIG. 3A is a plan fragment of a typical prior plate which is FIG. 4 isan enlarged vertical section through the stationary and rotating .discsand the supported refiner plates; and

FIG. 5 is a graph on which D,/D,, is plotted against hor-' sepower forvarious conditions.

THEORY OF REFINER OPERATION W The work put into a disc refiner, for thepurpose of analysis, can be broken into four main parts: (1) thehydraulic friction loss when'a disc rotates in a liquid; (2) the pumpingwork (loss) due to acceleration of the liquid to the exit velocity; (3)the mechanical friction loss due to friction in the bearings, etc. (thisitem is a small percentage of the total, and since it is a constant canusually be ignored); and (4) the work put into refining the stock.

Referring to the loss items 1, 2 and 3 above, only item I is of asubstantial nature, and its percentage to the total work can be reducedby proper consideration of the inside and outside diameter ratios of therefiner plates. The pumping work factor (item 2) need not be ignored,but in reality forms only about l- 2 percent of the total horsepowerinput into a refiner.

Referring to item 4 the present invention is the result of a newapproach to understanding the work put into the stock, by a directanalogy to the horsepower formula for an annular type clutch or discbrake. This factor will be developed below in greater detail.

THE FRICTION LOSS FACTOR H'P,,'='K.,N D

in which K is a constant, N is the speed of rotation, and D is the discdiameter. However, since the disc in a refiner is annular, the portionforming the loss may be expressed as a difference in diameter. Inaddition, it has been determined experimentally that the constant K, fora conventional bar and groove plate is at least three times as high asthat of a smoothplate. Therefore, the above formula can be written asfollows:

in which K N (D,, -Df) represents the losses in the bar and groove areaand represents the losses caused in the smooth area. It can be seen fromformula (2) that the larger the area having no bars and grooves, thesmaller will be the unproductive friction loss. Since the frictionlosses represent between 30-50 percent of the total power applied to thedisc refiner, any reductions in this loss may provide correspondingimprovements in the overall efficiency of the refiner. Accordingly, anyanalysis of refiner efficiency must include a consideration of the discfriction loss, as related to the total work input and as related to theeffective work applied to the refiner, as described below.

EFFECTIVE WORK As previously indicated, the present invention makes useof an analogy to disc type brakes and clutches for an understanding ofthe effective horsepower (HP applied to the stock. This is a validassumption due to the fact that in actual operation, the relativelymoving and stationary bars have an interface clearance of between .003and .010 of an inch, for example. The fibers which flow into the spacebetween the bars become stapled across the bars and exert an axial forcetending to separate the rotating and stationary elements, which is asubstantially greater force than the hydraulic forces within therefiner. They also exert a friction drag between the relatively rotatingelements not unlike that of an annular disc-type brake. Thus, in theoperation of a typical disc-type refiner, a pair of opposed stationaryplates are brought axially into working relation with opposite sides ofacenter rotating disc, and a clearance is established only during actualflow of the stock through the refiner, since the stock, and the fiberswithin the stock, maintain the necessary axial separating force toprevent physical contact and ultimate destruction of the relativelyrotating elements. A suitable control system for effect- 'ing control ofthe refiner plates, is shown and claimed in the copending application ofFrank Hayward, Ser. No. 698,931 filed Jan. 18, 1968 and assigned to theassignee of this application.

The remaining work put into the refiner, subtracting the loss itemsabove, is the effective useful work in refining the stock. It was foundthat the refining factor cannot be increased merely making furtherincreases in the area of the bar and groove pattern within a givenrefiner. Rather, the ratio of the effective power to the total can onlybe increased by properly selecting the DJD ratio of the bar-and-groovepattern.

In a disc brake, the horsepower which is dissipated is equal to aconstant, multiplied by the rpm. multiplied by the difference of thecube of the OD. and the cube of the ID. of the contacting surfaces,assuming that the forces between the plates are equal between the ID.and the OD, and can be written as follows:

HP =KeN(D., Di

The constant K, includes pressure in psi or other dimensions, andincludes the coefficient of friction.

Formula (3) applies when the refiner plates are new, and the pressureover the entire contacting surfaces is uniform. Refiner plates wear inuse, and the wear is a function of the work performed and isproportional to the product of speed, pressure, and coefficient offriction. Assuming the coefficient of friction remains constant, inorder to achieve uniform wear, the work expended must be constant overthe surface. How- 'ever, the linear speed varies directly with diameter,and thus the pressure tending to separate the plates must vary inverselywith diameter. Accordingly, at the inside diameter of the refiner platesthere is a condition of high pressure and low speed, generallyconsidered to be a cutting condition, while at the outside periphery ofthe disc there is a an area of high speed and lower pressure, consideredto be hydrating or fibrillating condition.

Formula (3) for a disc-type refiner, can be rewritten as follows:

K is a constant which includes the coefficient of friction between thefibers and the plate and fiber-to-fiber, and the available operatingpressure between the adjacent relatively rotating surfaces.

PLO'ITING THE EFFECTIVE WORK AND LOSSES AS A FUNCTION OF D /D The discfriction loss formula (2A) can be rewritten as follows:

Dividing each side of the equation (5) by a constant, the totalhorsepower (HPi), produces the following:

il HP, HP, 1 2/3 D,

The term K N D /HP,, in formula (6) is a constant when comparingrefiners of the same speed and diameter. Therefore, it will be seen thatthe ratio of disc friction horsepower HP to the total horsepower HP, isequal to a constant times a function of D,/D and may be written asfollows:

H P d i 5 HPJ 2/3 (51)] Where C is a dimensionless constant.

The function represented by formula (1) has been plotted on FIG. 5 bythe broken line 20, for a particular disc having a D fD ratio of 0.45 inwhich the constant C is an arbitrary 0.334. It will be seen by referenceto FIG. 5 that curve 20, at its right hand extent, approachesassymptotically a value of about 34 percent of the total power input,but drops off rapidly with D lD ratios greater than 0.5. A power savingcan thus be effected by choosing D lD ratios of greater than 0.5.

The effective horsepower can also be plotted against D /D,. Formula (5)can be rewritten as follows:

Dividing each side of the equation by HP, gives the following:

s-er] HP, HP, 1), Do (9) In formula (9) the term K ND /HP, is again adimensionless constant when comparing refiners of the same speed anddiameter. Therefore, formula (9) may be simplified as follows:

2 a HPF 1 (1).)

Where C is a dimensionless constant.

Formula (10) relates the ratio of effective-to-total horsepower in termsof D /D It is plotted on line 25in FIG. 5, again assuming the sameconditions as previously assumed, that is, assuming a value for theconstant C, of 1.87 which has been determined for conventional refiningplates having a DJD, ratio of 0.45.

EFFICIENCY The D lD ratio for maximum. efficiency does not coincideexactly with the maximum value for HP, at approximately .6 as plotted inFIG. 5, due to the fact that the friction loss factor HP, continues todecrease with increasing D,D ratio. The formula for efficiency 1; can bewritten as follows:

From formula 11 it will be seen that efficiency is a function of theeffective power HP divided by the sum of the effective power and thefriction power. All other terms in the efficiency formula are constants.Therefore, a curve can be-plotted of Again, as indicated above inconnection with formulas (6) and (9), the first term of the horse powerequation is a constant and has no bearing upon the derivative. Thus,equation (12) can be rewritten as follows in which the ratio ofeffective horsepowcr to disc loss horsepower is defined as a function ofa -(an Differentiating and setting the first derivative of the equationto zero and solving for D,/D,, given a D,/D,, optimum of 0.64. The curvefor formula (13) is plotted at in FIG. 5 in which it will be seen thatthe optimum portion at the top is relatively flat, and near maximumefficiency is obtained for D lD, ratios of between 0.55 and 0.85.

DESCRIPTION OF PREFERRED EMBODIMENT The teachings of the invention havebeen applied to a disctype refiner in FIG. 1. The refiner 35 includes arotatably mounted shaft 36 upon which a central disc 38 is mounted forrotation between a pair of axially adjustable nonrotating plates 39 and40. The refiner plates are contained within a housing 42 with twininlets 43 and 44 into which the stock to be refined is admitted, and asingle outlet 45. The stock from the inlets 43 and 44 is applied to aregion adjacent the axis of the shaft 36, as shown in FIG. 2, and isthus directed to a region radially inwardly of the stationary androtating discs.

The rotating discs 38 and the stationary or nonrotating plates 39 andeach have mounted thereon refining plate structure, as shown in greaterdetail in FIGS. 3 and 4. The plates 39 and 40 are each mounted on a pairof transversely disposed arms 48 and 49. The arms are mounted in turn onoppositely threaded shafts 50, and are positionable by a drive mechanism52 to move in unison axially toward and away from the rotating disc 38.The drive mechanisms 52 are normally remotely and automaticallycontrolled, such as for example by the apparatus disclosed in theabove-identified copending application, to cause a predetermined load ona meter driving the shaft 36.

As mentioned above, the disc 38 and the adjacent plates 39 and 40 eachsupport annularly arranged refiner plate structure such as showngenerally at 60 in FIG. 3. The refiner plates are formed preferably as adirect substitute for prior refiner plates, such as that shown by thesegment of the plate 60a in FIG. 3A. Also, since the left-hand andright-hand refiner plates mounted in opposed working relation aresubstantially identical in construction that the plate. arrangement orassembly 60 is typical of each of the four sets of plates used in thetwin disc refiner 35.

The plate assembly 60 is formed with an outer annular arrangement ofarcuate refiner plate segments 65, each ofwhich is formed with a portionof a bar-and-groove pattern formed therein. The arcuate segments 65together make up a full annular ring of segments forming an annulararray of bar-andgroove pattern having the D and D, dimensions asindicated by the respective reference lines in FIG. 3.

The pattern as shown in FIG. 3 comprises parallel and generally radiallydisposed equally spaced bars 70 separated by intermediate grooves 71.The space between the bars 70 being about generally equal the width ofthe bars. Each bar is formed with a planar refining face surface 74which terminates at relatively sharp opposite edges 75, with axiallystraight walls leading into the grooves 71. The individual spacing ofthe bars, and the depth of the bars is mainly a matter of choice, withinthe preferred D,/D,, ratios of this invention.

Since the refiner plate construction of the present invention,incorporating the bar-and-groove pattern, comprises a relatively narrowradial space, the remaining space in a conventional refiner is completedin the preferred embodiment with a fill plate which is positionedradially inwardly of the plate segments 65. The fill plate 80 is formedwith a smoothly tapered face surface 82, which lends from a regionadjacent the outer circumference of the axle 36 into the bar-andgroovepattern, with the surface 82 terminating at a plane coincident with thebottoms of the grooves 71. The outer diameter of the fill plate 80 thuscoincides with the inner diameter of the assembled plate segments 65.When two of such fill plates 80 are mounted in opposed relation, asshown in FIG. 4, a smoothly tapered throat is formed between thesurfaces 82 for guiding the stock radially outwardly into the opposedbar-and-groove patterns for refining.

The arrangement of fill plates 80 defining the tapered leadin throattends to eliminate the reverse fluid coupling or circulatory flow whichoccurs between the planar spaced adjacent surfaces of two relativelyrotating plates. Obviously, the occurrence of such counterflow isundesired since it impedes the desired movement of the fibers into thepattern area where it is acted upon by the opposed bars during rotation,for ultimate disposal outwardly of the housing 42 were it is accumulatedfor exit through the discharge opening 45 In some instances, it may notbe desirable to form the fill plates 80 as separate annular plateinserts. For example, some refiners may not have provision for mountingand supporting a separate plate, and in those instances, it may bepreferred to extend each of the arcuate refiner segments or assemblies60 radially inwardly beyond the above-defined critical bar-andgroovepattern limit to form a smooth throat or lead-in surface correspondingto the surface 82 provided by the annular plates 80. Also, it is withinthe scope of this invention to design the refiner discs 38 and backupplates 39 and 40 to form integrally the lead-in throat surfaces 82defined by the plates 80, since these areas are subject to very little,if any, wear, and may accordingly be provided as a more permanent partof the refiner.

While the invention will normally be employed for the refining of paperstock, it is within the scope of this invention to apply the teachingsthereof to disc-type refiners in general, which may be used for varioustypes of cellulosic fibrous material, for cutting and/or refining suchmaterial, including but not limited to bagasse, cotton, insulation boardfiller materials, and the like.

The invention accordingly provides a disc-type refiner and plates forsuch a refiner having improved refiner efficiency with correspondingdecreased power requirements. The barand-groove pattern on the plateassembly 60 comprise the working portion of the refiner plates and isrelated to the smooth lead-in portion of the refiner plates so that thebarand-groove pattern defines and extends over only a predetermined andcritical fraction of the total diameter of the combined plates 60 and 80to provide a greater efficiency in the refining action of the workingportions. The preferred ratio of diameters of the smooth to the workingportions is in the range of0.55 to 0.85.

The plate assembly 60 may be employed as direct replacements for' platessuch as that illustrated at 60' in FIG. 3A presently used in refiners,with a resulting improvement in operating efiiciency as depicted in thegraphs of FIG. 5. The bar-and-groove refining patterns of the presentinvention are subject to more uniform radial wear, since they occupy amore restricted and more precisely defined radial range, and since thewear is more uniform the plates tend to last longer before replacementis necessary.

While the form of apparatus herein described constitutes a preferredembodiment of the invention, it is to be understood that the inventionis not limited to this precise form of apparatus and that changes may bemade therein without departing from the scope of the invention which isdefined in the appended claims.

We claim:

1. A disc-type refiner for fibrous cellulosic stock having improvedrefiner efficiency with decreased power requirements, comprising arefiner housing having a stock inlet and an outlet, at least one annularstationary plate and an adjacent rotating plate, the adjacent annularfaces of each plate having means defining an inner relatively smoothportion and an outer working portion, said working portion being formedwith a pattern of alternate bars-and-grooves for receiving stock fromsaid inlet, refining the stock therebetween, and for discharging thestock in a radially outward direction, the smooth portions of the platesextending radially outwardly over more than a predetermined criticalfraction of the diameter of the plates to provide for reduced loss ofpower and greater efficiency in the refining action of said workingportions, the ratio of the diameters of the smooth portions to thediameters of the working portions being in the range of 0.55 to saidpattern.

3. The refiner of claim 2 in which at least one of said fill plates isformed with a radially tapered'surface defining said throat ofdecreasing width with increasing radial distance and terminating at thebase of said grooves; i

4. An improved refiner plate fora disc-type paper pulp refiner,comprising a plurality of arcuate plate segments each having a portionof an annular bar-and groove pattern formed thereon adapted for assemblyon a backing support in a refiner and together defining a full annularbar-and-groov'e pattern in which the ratio of inside diameter tooutsidediameter of said pattern is between 0.55 and 0,85.

5. The refiner plate of claim 4 further comprising means defining a fillplate having an outer circumference which coincides with the innercircumference of s'aidsegments and having a generally smooth radiallydisposed surface leading into said bar-and-groove pattern, and in whichthe portion of said surface adjacent said arcuate segments is in generalalignment with the bottoms of the grooves of said pattern.

222 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3552 554 Dated January 2' 191;

Inventor(s) William Herbert and James H. Riedel It is certified thaterror appears in the above-identified patent and that: said LettersPatent are hereby corrected as shown below:

Column A, line 29, X1) should be (7) Column 5, line 3, "HP /HP /D valuefor shouldbe -HP /HP is a maximum.

The corresponding D /D value for-- Column 5, line 28 "given" should be--gives- Signed and sealed this 1 0th day of August 1971 (SEAL) Attest:

EDWARD M.FI.|ETCHER,JR. WILLIAM E. SCHUYLER, J1 Commissioner of PatentAttesting Officer

2. The refiner of claim 1 in which said smooth portions comprise a pairof oppositely-disposed fill plates positioned radially inwardly of saidbar-and-groove pattern forming a throat leading from a region adjacentthe axis of said refiner rotor to said pattern.
 3. The refiner of claim2 in which at least one of said fill plates is formed with a radiallytapered surface defining said throat of decreasing width with increasingradial distance and terminating at the base of said grooves.
 4. Animproved refiner plate for a disc-type paper pulp refiner, comprising aplurality of arcuate plate segments each having a portion of an annularbar-and-groove pattern formed thereon adapted for assembly on a backingsupport in a refiner and together defining a full annular bar-and-groovepattern in which the ratio of inside diameter to outside diameter ofsaid pattern is between 0.55 and 0.85.
 5. The refiner plate of claim 4further comprising means defining a fill plate having an outercircumference which coincides with the inner circumference of saidsegments and having a generally smooth radially disposed surface leadinginto said bar-and-groove pattern, and in which the portion of saidsurface adjacent said arcuate segments is in general alignment with thebottoms of the grooves of said pattern.